1. Field of the Invention
The present invention relates to an apparatus for curing silicone rubber used with piezoelectric components or other electronic components, wherein after the periphery of piezoelectric element is covered with silicone rubber, the surrounding areas thereof are covered with an armoring resin.
2. Description of the Related Art
A conventional piezoelectric component is disclosed in Japanese Unexamined Patent Application Publication No. 1-228310, for example, wherein the periphery of a piezoelectric element having lead terminals attached thereto is covered with an elastic material such as silicone rubber and surroundings thereof are sealed with an armoring resin. The silicone rubber prevents changes in vibration characteristics of the piezoelectric element due to the contractile stress of the armoring resin and a damping effect on the restraining waveform distortion of the piezoelectric element as well.
In order to manufacture such a piezoelectric component, piezoelectric elements are attached to a lead frame, the periphery of the piezoelectric element is coated with silicone rubber by dipping it such that the lead frame is held by a jig so as to be heated and cured in an oven, then an epoxy resin is coated therearound by dipping it such that the lead frame is held by the jig so as to be heated and cured again in an oven and so as to define an armoring resin layer. Then the lead frame is removed from the jig and the piezoelectric component is obtained by separating lead terminals from the lead frame. In such a manner, mass-productivity is increased and uniform quality of the products is obtained as well by subjecting a plurality of piezoelectric elements, which are continued to be held by the jig, to the series of processes.
When the thermosetting silicone rubber is heated and cured in an oven, it is generally heated at a temperature in a range of 150xc2x0 C. to 160xc2x0 C. range, for 30 minutes to 1 hour by utilizing direct heat transmission of hot air. However, when a piezoelectric element (a piezoelectric ceramic element, for example) is exposed to such a high temperature for a long time, there is a problem that piezoelectric characteristics are degraded (dipole).
In such methods that the silicone rubber coating and the armoring resin forming processes are performed while a plurality of piezoelectric elements are held on a jig as described above, during the heating and curing in an oven, the jig as well as piezoelectric elements must be heated because the jig holding the piezoelectric elements is inserted into the oven. Since the thermal capacity of the jig is much greater than the thermal capacity of the piezoelectric elements, the jig requires a heating time and it also requires a cooling time after being removed from the oven, so that there is a problem that a long time is required for the curing process of the silicone rubber.
Furthermore, in the conventional heating and curing apparatus having a heater and a fan, the equipment must be relatively scale, resulting in a problem of high cost when including a conveying system.
In order to overcome the problems described above, preferred embodiments of the present invention provide a curing method and a curing apparatus wherein heating and curing processes are performed very quickly and without degrading the characteristics of the piezoelectric element so as to improve productivity of electronic component manufacturing.
In accordance with a first preferred embodiment of the present invention, a method of curing silicone rubber includes the steps of holding a plurality of piezoelectric elements in a jig, coating silicone rubber on external surfaces of the piezoelectric elements held by the jig, and irradiating the uncured silicone rubber coated on the external surfaces of the piezoelectric elements with far infrared rays so as to cure the silicone rubber.
In accordance with a second preferred embodiment of the present invention, there is provided a curing apparatus for silicone rubber for curing the silicone rubber coated on external surfaces of electronic components such as piezoelectric elements, the curing apparatus including a jig for holding the piezoelectric elements having the uncured silicone rubber coated on the external surfaces thereof, and having the property of reflecting far infrared rays, and a far-infrared-ray generating unit for irradiating the uncured silicone rubber coated on the external surfaces of the piezoelectric elements with far infrared rays so as to cure the silicone rubber.
According to preferred embodiments of the present invention, after the external peripheral surface of piezoelectric element is coated with the uncured silicone rubber in the state that plurality of electronic components are supported in a jig, the jig is transported to a far infrared generating unit. When the piezoelectric elements are irradiated with far infrared rays generated in the far infrared generating unit, the far infrared rays are selectively absorbed into the silicone rubber coated on the electronic components while they are not substantially absorbed in the jig and the electronic components. Therefore, the electronic components, e.g., piezoelectric elements do not produce heat, and degradation (dipole) of piezoelectric characteristics is thereby prevented. Also, the jig having a large thermal capacity does not produce heat, so that the time for heating and the period for cooling after the curing process is greatly reduced. Since in the silicone rubber, heat is produced from the inside thereof by far infrared rays, the curing proceeds evenly, so that the entire silicone rubber can be uniformly cured.
Preferably, the far infrared rays emitted from the far infrared generating unit include wavelengths of about 7 to about 15 xcexcm. The range of the wavelengths is generally 5 xcexcm to 1000 xcexcm, and among the wavelengths, the absorption spectrum of the silicone rubber exhibits the highest level in the wavelengths of about 7 xcexcm to about 15 xcexcm. By irradiating the silicone rubber with the far infrared rays including this wavelength range, the far infrared rays can be effectively absorbed into the silicone rubber while not being absorbed in the electronic components and jig, and the thermal efficiency is thereby improved.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the attached drawings.